1. Field of the Invention
The present invention relates to a semiconductor light emitting device using group III nitride semiconductor.
2. Description of the Related Art
In recent years, there have been increased demands for semiconductor laser diodes capable of outputting blue violet light as a light source for next generation high-density optical disks. Thus, an increased number of research and development of group III nitride semiconductor, i.e., direct energy-gap semiconductor having a forbidden band of 1.9 eV to 6.2 eV have been carried out.
Among light emitting devices including group III nitride semiconductor, to increase confinement of light and suppress dispersion of magnesium (Mg) from a p-type cladding layer to an active layer, a laser diode is formed to have a structure in which an optical guide layer and an intermediate layer are formed between the active layer and the p-type cladding layer. Furthermore, there are cases where in order to suppress overflow of electrons from the active layer to the p-type cladding layer, an electron blocking layer made of a material having a smaller electron affinity than those of the intermediate layer and the p-type cladding layer is provided immediately under the p-type cladding layer. To realize a highly reliable blue violet laser diode, a low threshold current is necessary. Therefore, it is very important to sufficiently suppress overflow of electrons from the active layer.
Hereafter, a known group III nitride semiconductor laser diode will be described. FIG. 10 is a cross-sectional view illustrating a structure of the known group III nitride semiconductor laser diode.
As shown in FIG. 10, the known group III nitride semiconductor laser diode includes an n-type contact layer 102 epitaxially grown on a sapphire substrate 101, an n-type cladding layer 103 provided on the n-type contact layer 102, an undoped n-side light guide layer 104 provided on the n-type cladding layer 103, a multi-quantum well (MQW) active layer 105 provided on the undoped n-side light guide layer 104, an undoped p-side light guide layer 106 provided on the MQW active layer 105, an undoped first intermediate layer 107a provided on the undoped p-side light guide layer 106, an undoped second intermediate layer 107b provided on the undoped first intermediate layer 107a, a p-type electron blocking layer 108 provided on the undoped second intermediate layer 107b, a p-type cladding layer 109 provided on the p-type electron blocking layer 108 and having a convex portion and a p-type contact layer 110 provided on the convex portion of the p-type cladding layer 109. The known group III nitride semiconductor laser diode further includes an insulating film 111 provided over the substrate so as to cover part of an upper surface of the n-type contact layer 102 and side surfaces of the n-type cladding layer 103, the undoped n-side light guide layer 104, the MQW active layer 105, the undoped p-side light guide layer 106, the undoped first intermediate layer 107a, the undoped second intermediate layer 107b, the p-type electron blocking layer 108, the p-type cladding layer 109 and the p-type contact layer 110, a p-side electrode 112 provided on the p-type contact layer 110, and an n-side electrode 113 provided on the n-type contact layer 102 (for example, see Japanese Laid-Open Publication No. 2003-289176).
Next, the electron overflow suppression effect by an electron blocking layer will be described.
FIG. 11 is a conduction band diagram in main part of the known semiconductor laser diode of FIG. 10. The p-type electron blocking layer 108 is formed of a material having a smaller electron affinity than those of the intermediate layers 107a and 107b and can suppress overflow of electrons to the p-type cladding layer 109 with a conduction band edge barrier.